1. Field of the Invention
The invention relates to the structure and assembly of data storage devices. Specifically, the invention relates to a disk drive architecture which facilitates use of a completely automated assembly process.
2. Description of the Related Art
Storage technology has followed a trend of increasing storage capacity while simultaneously decreasing the amount of physical space required to maintain such capacities. With the advent of ever more powerful computer microprocessors and software which can take advantage of the microprocessors, obtaining additional storage space at a reasonable cost per unit of storage is a paramount concern for storage device manufacturers. Indeed, market pressures have driven the monetary cost per unit of storage downward thereby placing greater demands on manufacturers to reduce drive costs. In order to maintain a market advantage, new storage device designs incorporate greater efficiency in both device operating tolerances and manufacturability. Currently, storage device manufacturers strive to achieve every bit of cost per unit of savings which can reasonably be achieved without sacrificing technical performance.
A key aspect in reducing the cost of storage devices is in improving the manufacturability of components. Storage devices generally include a storage medium for the data, read/write heads for recording and retrieving the data from the storage medium, a controller which positions the heads with respect to the storage medium and directs the recording and retrieval of data therefrom, and a conductor assembly for electrically interconnecting the heads, actuator and controller.
There are several formats for storage devices, including "flash" memory cards which store data as programmed digital data in electrically charged silicon, and optical or magnetic disk storage devices which store data on a rotating media. In disk-type storage devices, storage disks are generally rotated in a housing while a read/write head, either an optical head or a magnetic head, transfers data to and from the storage medium. Such heads are positioned with respect to the storage medium by an actuator between an inner circumferential limit, the inner diameter or "ID", and an outer circumferential limit, the outer diameter or "OD". A voice coil motor, comprising a magnet and coil assembly or a stepper motor, may be used to position the actuator and heads with respect to the disk storage medium.
Such actuators may be linear or rotary, each having specific advantages in the particular application used. In magnetic disk drives, rotary actuators have become somewhat prevalent in usage. In general, a rotary actuator assembly includes a cast or extruded side-facing "u" or E-shaped block (generally referred to as the E-block), usually made of aluminum or magnesium, to which suspensions or which support the read/write elements are attached. The E-block rotates about an axis perpendicular to the major surface of the disks and closely adjacent thereto, and is either coupled to a portion of a stepper motor or, more commonly, carries a portion of the voice coil motor. The E-block consists of: a cylindrical section into which a bearing assembly is installed; two, three, or any number of identical and aligned arms, extending from the cylindrical section at evenly spaced distances apart, to which the load beams are attached; and some form of attachment for a stepper motor or voice coil motor component.
The manufacture of a Winchester-type magnetic disk drive is accomplished on a drive assembly line where components such as the spindle motor, storage disk, actuator, header assembly and flexible circuit are affixed to the base, the cover installed and the drive sealed. This process is performed by a variety of manual and automated sub-processes. The assembly operation is performed in a class 100 clean room environment to reduce, to the greatest extent possible, the amount of contamination which is provided into the internal housing of the disk drive. Such contamination may interact with the head/disk interface and other components thereby acting to cause drive failure.
Many of the component parts, such as the spin motor, actuator, disk, header and flex-circuit are preassembled by component vendors and provided to the drive manufacturer. These parts are thereafter assembled by the manufacturer using the aforementioned combination of automation and manual labor.
The performance of a disk drive is measured by many factors, including the average seek time, the storage capacity, and the data throughput in MB/second. To a large extent, the drive manufacturer incorporates these performance factors into account in achieving the desired design goals of a particular device design. Mechanical and electrical design tolerances are specified to values within pre-defined tolerances. For components which are turned over to outside vendors for manufacture, or "out-sourced" components, a quantum of error in both the number of parts which meet the design specification, and how well those parts meet the design specification, is anticipated in the design. These imperfections will affect the overall design performance of the drive and, if serious enough, production yields, due to component failure.
In manufacturing rotary actuators, the E-block, usually made of aluminum or magnesium, is cast or extruded as a singular block element and machined to provide attachment points for the suspensions, bearing assembly and latch components, and stepper motor or voice coil motor component attachment. The suspensions are attached to the E-block by swaging or staking through machined bores in the E-block arms so that the read/write elements are in vertical alignment over the disk. It is extremely important that the tolerances of the E-block, suspensions and head alignment be accurately maintained.
The swaging process used for attachment of the suspensions to the E-block arms is a process whereby the arm and a suspension member to be joined to the arm are positioned adjacent to each other, each with a like-sized bore at the joinder location, after which a steel ball bearing is forced through the respective bores.
Several problems are noteworthy with this approach. First, the cost of manufacturing the E-block is rather high. Each E-block is the result of a casting mold which must be made to specification for each drive. Second, the suspensions must be individually attached and aligned to the E-block. Generally, the read/write heads are attached to flexures on the suspensions prior to assembly of the suspensions and the E-block. Alignment of the heads and the suspensions into a vertical stack must occur when the beam is attached to the E-block. Further, it is difficult if not impossible to maintain the preset spring rate and gram load of the suspensions during the swaging process. The alignment and staking of the suspensions and heads must be supervised and monitored by a human being, thus increasing the cost and decreasing the speed of assembly of the drives.
As is generally well known, if the recording technology employed is that of a magnetic hard disk drive, each head includes a slider body and a recording gap which is on the order of 5 microns in length. In an "air bearing" disk drive, the slider body lifts off the surface of the storage medium and "flies" over the surface of the disk on a very small cushion of air. It is very important in such drives that the distance between the head and the disk be maintained at an accurate level. Currently, head to disk spacing (or "flying height") is on the order of 2-4 microinches, and maintaining such distance at a constant level is extremely difficult. Thus, while the optimal drive design may call for a nominal flying height of 4 microinches, the drive design accommodates a variance of up to 1-2 microinches in the flying height to ensure the head will not "crash" into the disk.
To maintain such heights, each suspension has a specific spring force. This spring force provides resistance to excess movement of the head away from the disk when the air cushion lifts the head from the disk upon disk rotation. The spring force or "gram load" complicates the design and fabrication operations, and can be inadvertently altered during the process of attaching the suspensions to the E-block.
An alternative to the E-block and stacking assembly described above is a unitary mounted suspension and mounting assembly, such as that disclosed in U.S. patent application Ser. No. 07/757,789, filed Sep. 11, 1991, inventors F. Mark Stefansky, Louis J. Shrinkle, and Thomas A. Fiers, owned by the owner of the instant application and hereby incorporated by reference. In such an assembly, the suspension is welded to an actuator armplate which is secured to spacers and other such arm assemblies in a rigid manner to form the actuator assembly. A similar structure is manufactured by Hutchinson Corporation and marketed under the name Hutchinson "Unamount" suspension. The actuator arm plate includes a circular bore which, when coupled to the spacer elements, forms a cylindrical bore designed to receive a bearing assembly.
The use of the unitary suspension and actuator arm suspension system alleviates the stacking process required to attach the suspension to the actuator arm, but raises additional issues in the form of securing the suspensions together in a format which is rigid enough to resist shock and vibration at the design specifications of the drive. In application Ser. No. 07/757,789, this problem is solved by providing a number of fasteners which secure the stack together at various locations about the bearing cartridge.
In the conventional assembly process for disk drives wherein out-sourced component parts of the drive are assembled by the manufacturer, not all of the out-sourced components meet the specifications called for by the manufacturer and can reduce final product yields. It would be most advantageous if individualized drive components could be accurately tested prior to installation in the drive to determine whether the tolerances have been met. With some components, such as actuator bearing cartridges, this is possible; however with pre-assembled actuators, it is generally not possible to test the alignment of the head with respect to the head stack.
For example, in magnetic recording technology, the read/write heads are generally fixed to the suspension by a head vendor and shipped to an actuator vendor which couples the suspension/head assembly to the E-block. This assembled actuator arm is then provided to the disk drive manufacturer. As noted above, the alignment of the head gap with respect to the suspension and other gaps in the head stack is important in terms of the track-to-track alignment of the heads on adjacent disks and on alternating sides of the same disks. In this arrangement, alignment of the head gaps once the heads are attached to the E-block is subject to error at the actuator vendor. This error must be compensated for in the drive controller electronics. Additionally, the purchase of this assembly from a vendor represents a significant part of the total cost of a drive.
A further part of the assembly process involves electrically interconnecting the controller to the heads and the actuator in a manner which is reliable and cost efficient from a functional and a manufacturing point of view. Currently, because of the nature of magnetic read/write heads, the heads are electrically coupled to very small gauge lead wires which run along the length of the actuator arm to a molded, flexible circuit (or flex circuit). The flex circuit comprises electrical conductors encased in a flat molded plastic casing which is secured to the actuator and to a bracket, or other fixture, in the drive housing. Electrical coupling of the head wire leads to the flex circuit takes place by soldering the leads to conductive solder pads formed on the flex circuit. In some drives, the flex circuit is formed to attach to a portion of the actuator body, usually the cylindrical portion of the actuator body, and aligned so that the solder pads are at a point on the cylindrical body where the leads need only run down the arm to the point where the arm meets the cylindrical portion of the body to attach to the solder pads.
The conventional assembly operation of the actuator is a manually intensive operation. The attachment of the head wire leads to the flex circuit must be performed manually as no effective means has yet been found to automate the attachment process. The process involves manually aligning the head wires with the solder pads on the flex circuit and attaching the wires to the flex circuit solder pads through the use of solder. Further, as noted above, the staking or swaging process requires manual alignment of the heads and suspensions on the E-block, and increases the chance that the suspensions could be damaged during assembly.
In addition, placement of the bearing assembly into the actuator, routing of the flex circuit leads, and coupling of the leads with respect to the actuator are performed manually. As will be readily recognized, each manual step performed in any manufacturing process adds time to the process, and adds to the potential for head damage. Each of these factors can adversely impact production yields and increase the cost per unit of storage for the storage device.